The invention relates to radio frequency (RF) driver plasma ion sources, and more particularly to the RF antenna and the plasma chamber.
A plasma ion source is a plasma generator from which beams of ions can be extracted. Multi-cusp ion sources have an arrangement of magnets that form magnetic cusp fields to contain the plasma in the plasma chamber. Plasma can be generated in a plasma ion source by DC discharge or RF induction discharge. An ion plasma is produced from a gas which is introduced into the chamber. The ion source also includes an extraction electrode system at its outlet to electrostatically control the passage of ions from the plasma out of the plasma chamber.
Unlike the filament DC discharge where eroded filament material can contaminate the chamber, RF discharges generally have a longer lifetime and cleaner operation. In a RF driven source, an induction coil or antenna is placed inside the ion source chamber and used for the discharge. However, there are still problems with internal RF antennas for plasma ion source applications.
The earliest RF antennas were made of bare conductors, but were subject to arcing and contamination. The bare antenna coils were then covered with sleeving material made of woven glass or quartz fibers or ceramic, but these were poor insulators. Glass or porcelain coated metal tubes were subject to differential thermal expansion between the coating and the conductor, which could lead to chipping and contamination. Glass tubes form good insulators for RF antennas, but in a design having a glass tube containing a wire or internal surface coating of a conductor, coolant flowing through the glass tube is subject to leakage upon beakage of the glass tube, thereby contaminating the entire apparatus in which the antenna is mounted with coolant. A metal tube disposed within a glass or quartz tube is difficult to fabricate and only has a few antenna turns.
U.S. Pat. Nos. 4,725,449; 5,434,353; 5,587,226; 6,124,834; 6,376,978 describe various internal RF antennas for plasma ion sources, and are herein incorporated by reference.